(GPS: N37° 55.660 W119° 02.760)
Around 40, 000 years ago volcanic eruptions started to occur here in the Mono area and further south near Mammoth, CA (The Mono-Inyo Craters). Panum Crater is relatively recent with its eruption taken place around 650 years ago. What you see above is the inner circle of the crater. I started the hike going on the "rim trail" around the rim of the crater.
Let me try to explain this by just rehashing what I have read since I am not a geologist or scientist of any sort. Magma rose up and reached the cool water which created an explosion that produced the crater you see above and below. Afterwords, more magma (lava when it reaches the surface) came up in the middle part of the crater creating the inner dome part you see.
I headed back and went to the "plug trail" which takes you inside the intermost dome of the crater. You come out and in an "otherworldly" type of area:
There are lots of these spires around... 
Tons of obsidian and pumice around...
This area reminds me of a fantasy movie or something you might see in the Lord of the Rings books/movies.
It is one of those areas that I am not sure if videos and pictures do it justice, but it is out of this world! If I were to change the backgrounds in these pictures it might look like I was on another planet.
A few other links for further information: 
